Expression of p63 in the mouse primordial germ cells

Proteins encoded by p63 gene a have structural similarity with tumor suppressor p53, and were thought to induce cell cycle arrest and apoptosis during development. The p63 proteins are also expressed in the basal cells of many epithelial tissues in the adult, and supposed to play important roles in maintaining the epidermal stem cells. Previously, we reported the p63 expression in the testis of mouse embryos, suggesting their involvement in the growth arrest and apoptosis of testicular germ cells (Nakamuta and Kobayashi, J. Vet. Med. Sci. 65:853-856). In this study, we investigated the timing of this p63 expression in the germ cells during migration and colonization to the gonads. Immunohistochemical analysis of mice from embryonic day (E) 7.5 to E12.5 demonstrated that p63 positive reactivity was seen as early as E8.5 when the founder cells of germ cells, primordial germ cells (PGCs), were located in the hind gut epithelium, but PGCs were negative for p63 at E7.5 when they first appeared. p63 is expressed as six isoforms, resulting from alternative splicing at C-terminus and by the use of two promoters that generate variations at N-terminal end. RT-PCR analyses suggested that different types of p63 mRNAs were likely to be expressed in PGCs during development. These results imply that p63 may be involved in the regulation of PGC development by controlling the gene expression required for their migration and colonization to the gonads.